Abstract
Understanding how the brain allocates resources to match the demands of active neurons under physiological conditions is critically important. Increased metabolic demands of active brain regions are matched with hemodynamic responses known as neurovascular coupling (NVC). Several methods that allow noninvasive assessment of brain activity in humans detect NVC and early detection of NVC impairment may serve as an early marker of cognitive impairment. Therefore, non-invasive NVC assessments may serve as a valuable tool to detect early signs of cognitive impairment and dementia. Working memory tasks are routinely employed in the evaluation of cognitive task-evoked NVC responses. However, recent attempts that utilized functional near-infrared spectroscopy (fNIRS) or transcranial Doppler sonography (TCD) while using a similar working memory paradigm did not provide convincing evidence for the correlation of the hemodynamic variables measured by these two methods. In the current study, we aimed to compare fNIRS and TCD in their performance of differentiating NVC responses evoked by different levels of working memory workload during the same working memory task used as cognitive stimulation. Fourteen healthy young individuals were recruited for this study and performed an n-back cognitive test during TCD and fNIRS monitoring. During TCD monitoring, the middle cerebral artery (MCA) flow was bilaterally increased during the task associated with greater cognitive effort. fNIRS also detected significantly increased activation during a more challenging task in the left dorsolateral prefrontal cortex (DLPFC), and in addition, widespread activation of the medial prefrontal cortex (mPFC) was also revealed. Robust changes in prefrontal cortex hemodynamics may explain the profound change in MCA blood flow during the same cognitive task. Overall, our data support our hypothesis that both TCD and fNIRS methods can discriminate NVC evoked by higher demand tasks compared to baseline or lower demand tasks.
Highlights
IntroductionActivation of neurons in the brain implies the allocation of resources and nutrients by the cerebrovascular system
Under cognitive workload, activation of neurons in the brain implies the allocation of resources and nutrients by the cerebrovascular system
We aimed to investigate whether (1) activation of other areas in the prefrontal cortex can be measured with near-infrared spectroscopy (NIRS), (2) whether these areas are only activated at higher cognitive workload, (3) and compare the sensitivity of transcranial Doppler (TCD) and functional near-infrared spectroscopy (fNIRS) in their capabilities of detecting cognitive states evoked by different levels of cognitive workload during a working memory task
Summary
Activation of neurons in the brain implies the allocation of resources and nutrients by the cerebrovascular system. Recent studies suggested that decreased cognitive performance may be associated with increased or decreased cortical NVC responses during certain cognitive tasks [2, 3], depending on the type and difficulty of the task. These recent developments highlight the importance of further investigations of NVC to better understand the resource allocation of the brain while performing cognitive tasks under physiological conditions
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